I edge usually once a year using a blade edger (hand helds and walkbehind)
and utilize a line trimmer to maintain the illusion along
sidewalks and around tree circles for the rest of the year.
It's an artform and some employees are
masters at it.
Some-times we deep edge gardens with a square shovel. It depends on the site.

We have the B.C. Landscape Standard that suggests we could do a hard edge with a
blade edger say, twice a year.

Some of the companies here have a dedicated employee that goes around every week
like an artist, and redefines the edges.
Larger properties contracts are worded so that half of the site will be done one
week and the other half the second week, as required.

Unless some-one or some-thing has destroyed the edge space,
I would rather save time and just use a line trimmer.
I can really get the same look either way

We use string trimmer turned 90 degrees. we can create a defined edge in the middle of the lawn if the customer wants...Trick is big power heads on string trimmers and good line. We prefer the gator line with nylon in the center. Beds are edged every week to 2 weeks depending on usage areas.